The present invention relates to an image producing apparatus used primarily for an electro-photographic copying machine, printer, and facsimile.
A well known conventional image producing apparatus has image producing devices such as a primary corotron, image exposure, developer, transfer corotron, and cleaner around an image carrier. The surface of the image carrier is uniformly charged by the primary corotron and then an image is exposed to i.e. the surface to form an electrostatic latent image thereon. The electrostatic latent image is then developed by the developer into a visual image which in turn is transferred by the transfer charged corotron onto a sheet of paper. The paper is then fed to a fixer to be fixed. Then, residual is cleaned off the image carrier by a cleaner.
Such conventional image producing apparatus do not provide good reproducibility of an original having continuous gradation such as photographs, and therefore a construction as shown in FIG. 22 is used to improve reproducibility.
A screen lamp 6 formed of a screen 4 and a light source 5 is disposed between an image exposure 2 and a developer 3 behind a belt type photoreceptor 1. An original image is exposed by the image exposure 2 onto the surface of the belt type photoreceptor 1 uniformly charged by the corotron 7 to form a latent image thereon. Then, a screen-like optical image is projected by the screen lamp 6 onto the rear surface of the belt type photoreceptor 1 to form a screen-like non-charged portion so as to form an electrostatic latent image into fine stripes. Then, the electrostatic latent image is developed by the developer 3 into a visual image so as to reproduce an image of the original with continuous gradation.
With the above-described apparatus, the cavity latitude between the screen 4 of screen lamp 6 and the belt type photoreceptor 1 is important so that the screen lamp 6 must be accurately positioned relative to the belt type photoreceptor 1. The mounting of the screen lamp 6 is not only time-consuming but also difficult when replacing the screen lamp 6.
With an image producing apparatus (referred to as copying machine hereinafter) using the prior art electrophotography method, a uniformly charged image carrier(referred to as photoreceptor or photosensitive material hereinafter) is exposed to a light that carries the image of an original, so that a latent image is formed on the photographic body. The latent image is developed with a toner to produce a toner image which in turn is transferred onto an image-transferred material (referred to as paper hereinafter). The toner image is then fixed to provide a hard copy. The formation of a latent image, development of the image, and transfer of the developed image are carried out on the same sheet of paper for each color component to provide a full color copy.
Such an electrographic copying machine will not reproduce the same gradation (degree of brightness) as the original image, when producing a picture-like image such as photographs. Thus, it is difficult to produce an image having the same quality as the original. In which case, the photographic body is uniformly charged, and then a pattern image consisting of a net or a plurality of lines are formed for improved gradation of a copy.
Japanese Patent Preliminary Publication No. 62-103663 discloses a prior art pattern exposing apparatus that produces a pattern formed of a plurality of lines. This pattern exposing apparatus has a pattern plate in the vicinity of the photoreceptor, the pattern plate being made of a transparent material such as glass whose surface is printed through photomechanical process with a pattern having light-transmitting parts arranged alternately with non-light-transmitting parts. An incandescent lamp such as a tungsten bulb is provided at a position relatively remote form the pattern plate. In the light path between the incandescent lamp and the pattern plate is provided a shutter for intercepting the light. The thickness of the pattern printed on the pattern plate is on the order of several microns, In order that the pattern-carrying lights transmitted through the pattern plate are uniform in the direction transverse to the movement direction of the photographic body, the incandescent lamp should be remote from the pattern plate so that the lamp can be regarded as a point source. Since incandesdent lamps cannot be quickly turned on or off, the maps are lighted at all times and a shutter is placed in the light path to intercept the light so as to expose a pattern light only when the pattern light is required. This pattern exposing apparatus is referred to as a second prior art apparatus hereinafter.
Japanese Patent Preliminary Publication No. 64-61773 discloses an apparatus in which a pattern latent image is made with a net. This pattern exposing apparatus is provided with an image-forming lens which is mounted near a photoreceptor and extend transversely of the photoreceptor. The pattern exposing apparatus also has a pattern filter spaced apart from the image-forming lens, in which pattern filter a net pattern is formed in correspondence with a pattern to be formed. The apparatus further has light emitting diodes as a point source spaced apart from the pattern filter and means for controlling the on-and-off operation of the light emitting diodes. The light from the light source is converted into a pattern-carrying light by the pattern filter and is directed by the image forming lens to the surface of the photoreceptor. The control means controls the light to intermittently be emitted so as to form a net-like pattern latent image.
The provision of an image forming lens in the aforementioned manner permits the production of a substantially uniform pattern latent image even if the distance between the pattern filter and the light source is relatively short. This is referred to as a third prior art apparatus and is smaller in size than the aforementioned second prior art apparatus.
With the second prior art apparatus, the incandescent bulb should be positioned such that the incandescent bulb can be regarded as a point source. This leads to larger sizes of apparatus. A bulb must be capable of emitting a large amount of light so as to expose a sufficient amount of light onto the surface of photoreceptor because the incandescent bulb is remotely located. This requires a large amount of electric power. The light path must be selectively blocked by the use of, for example, a shutter. This leads to complex construction.
The above-described third prior art apparatus is further miniaturized than the second prior art apparatus. However, the apparatus includes a very expensive image-forming lens, being disadvantageous. Further, the apparatus is of a complex construction in which the on-and-off operation of the light source is controlled in synchronism with the movement of the photoreceptor.